This invention relates to pigment compositions for the coloration of plastics materials, said compositions being obtained by recycling the intaglio sludge. It relates further to the use of such pigment compositions for pigmenting PVC sheets and synthetic leathers and commodity and recyclable plastics, and related industries.
In the intaglio printing process, especially in the engraved steel die printing, the lines or points to be printed are etched or engraved in the surface of the printing plate or cylinder. To obtain prints, ink is applied to the face of the printing plate until all the depressions are filled, any excess ink then being wiped off. Sheets or webs of paper are passed onto the printing plate, and through the pressure of the impression cylinder, the paper is to some extent pushed into the intaglio depressions whereby the ink is transferred from the plate to the paper and thus printing is effected. The intaglio printing process is able to produce thick prints of delicate fine-lined patterns and is therefore ideal for printing banknotes and valued security paper such as traveller's cheques and high denomination postage stamps.
The excess ink wiped off during the intaglio printing usually comes down in a wiping vat in the form of colloidal suspensions in water or organic solvents such as trichloroethylene, depending on the printing ink used. In both cases, however, the suspension must be recovered as a waste sludge. It consists of residual pigments, residual ink resins, extenders such as titanium dioxide and calcium carbonate, and trace metal catalysts. All are ingredients of most plastics.
Intaglio sludges thus constitute solid waste pollutants. As practiced among security printers, they are disposed of in landfills. As the cost of landfilling is increasing, alternative methods are being sought.
It is obvious that the method of incineration as practiced in many industries is applicable to intaglio solid wastes. But incineration produces toxic gaseous pollutants which must be effectively trapped. This means added costly expenditure.
It is not difficult to see that intaglio sludges still possess good light and chemical fastnesses since they comprise good pigments requisite of quality security printing inks. In other words, good pigment properties remain unimpaired in the intaglio sludge. Thus, the sludge makes promising reclaimed pigments.